1. Field of the Invention
The general field of this invention is electronic printer technology. The present invention relates to pulse-width-modulation (PWM) circuits, image-forming apparatuses, and optical printing methods; and more particularly to pulse-width-modulation circuits for positional accuracy of modulated pixels on a printed page.
2. Description of Related Art
One limitation of typical current printer technology is that the application of ink or toner to a particular region of an image is essentially binary in nature—the printer may either apply toner or not. Modern printers typically use screens to generate smooth grayscales so that images and halftones can be reproduced accurately. Screens are typically used to build up a pattern of very small toner “dots” (e.g., laser on/off patterns) that when viewed by the naked eye give the illusion of a halftone.
To create a color image, some printers print an image as an overlay of four separate color planes: Cyan, Magenta, Yellow, and Key (black) (“CMYK”). For color screens, each color plane typically uses a different screen, and the screens may be offset with respect to one another. This screen angle offsetting technique is typically used to avoid the appearance of objectionable moire patterns in a final image.
The ability to left and right-justify pixels allows for more accurate control of the shape and size of printed dots. By combining the use of a pulse-width-modulation (PWM) device and a method of left and right-justification of pulse-width-modified pixels, additional control may be achieved. Pulse-width modification of pixels allows for more accuracy in a final image because it allows for the printing of partial pixels where a desired image occupies only part of a pixel space. Adding left and right-justification to pulse-width-modified pixels allows for partial pixels to be right-justified on the left edge of a halftone dot and left-justified on the right edge of a halftone dot, resulting in sharp edges and accurate printed representation of the desired halftone dot. Thus, there is a need for systems and methods for generating left and right-justified pulses and for adding such capabilities to existing PWM circuits.